1. Technical Field
The present invention relates to a variable magnification optical system and an imaging apparatus, and more specifically to a variable magnification optical system that can be used in video cameras, electronic still cameras, and particularly suitable for use as a surveillance camera application and an imaging apparatus equipped with the variable magnification optical system.
2. Background Art
As optical systems used in imaging devices, such as video cameras, electronic still cameras, surveillance cameras, and the like with image sensors such as CCD (Charge Coupled Device), CMOS (Complementary Metal Oxide Semiconductor), and the like as recording media, variable magnification optical systems for CCTV (Closed-circuit Television) have been developed. The variable magnification optical system for CCTV has an advantage that it is user friendly, for example, the focal length can be set according to the use environment, subject distance can be set on the user side, and the like. The CCTV optical system whose main purpose is surveillance needs to cover from a wide viewing area to the standard angle of view and withstand indoor and outdoor usages while being compact. For this reason, a negative-positive two-group variable magnification optical system composed of a negative first lens group and a positive second lens group which is relatively simple in configuration and satisfies these conditions is heavily used. For example, as negative-positive two-group variable magnification optical systems in which the first lens group is composed of four lenses of positive, negative, negative, and positive lenses and have a magnification ratio of about 3, those described in Japanese Unexamined Patent Publication No. 11 (1999)-160619, Japanese Unexamined Patent Publication No. 2000-035537, Japanese Unexamined Patent Publication No. 2001-330773, and Japanese Unexamined Patent Publication No. 2007-079108 are proposed.